1. Field of the Invention
The present invention relates to a vehicle lighting apparatus, and more particularly to a vehicle lighting apparatus that controls the lighting of a semiconductor light source composed of semiconductor light emitting elements.
2. Related Art
Conventionally, vehicle lighting fixtures using a semiconductor light emitting element, such as an LED (Light Emitting Diode), as a light source are well known. Vehicle lighting fixtures of this type have a lighting control circuit for controlling the lighting of the LED.
A lighting control circuit using a switching regulator capable of controlling the output voltage to the LED based on the current of the LED is well known. The switching regulator can control the output voltage to flow a specified current through each LED, even if a plurality of LEDs are connected in series or parallel as the load.
However, if the output of the switching regulator is short circuited, or has a ground fault, the switching regulator has a heavier load, and may fail with the excessive power load. Also, if the output of the switching regulator is opened due to a disconnection in the LED, the output voltage may be increased excessively, for example, in a switching regulator of a flyback type.
Thus, a switching regulator has been proposed in which, when a failure of the switching regulator on the output side is detected, the output voltage of the switching regulator is lowered (refer to patent document 1).
[Patent Document 1] JP-A-2004-134147 (pages 3 to 8, FIG. 1)
In the above prior art, a plurality of LED groups are connected in parallel on the output side of the switching regulator, a shunt resistor is connected in series to each LED group, the voltage across each shunt resistor is monitored by a failure detection part, the output voltage of the switching regulator is controlled so that the current of each LED group may become a specified value, and the output voltage of the switching regulator is lowered when the failure occurs, whereby even if some of the LEDs fail, the operating LEDs can be protected. However, there is no consideration of the case where a failure detection wiring that leads the connection point of each LED group and each shunt resistor to the failure detection part is disconnected.
That is, in detecting the failure of each LED group, where a connection point between each LED group and each shunt resistor is connected via a failure detection wiring to the failure detection part, when this failure detection wiring is disconnected, no signal is inputted into the failure detection part, even if the LED groups are normal. Thus, the failure detection part falsely detects a failure caused by opening the LED group. Consequently, the output voltage of the switching regulator is controlled to be lower even if the LEDs are normal.